DNA damage expressed as percent of tail DNA following exposure of the HK-2 cells to the ENPRA panel of engineered nanomaterials. The cells were exposed to cell medium (control), 60 μM H2O2 and NMs for 4 hr. Values represent mean ± SEM (n = 3), significance indicated by * = p < 0.05 and ** = p < 0.005, when material treatments are compared to the control. A) NM 300 B) NRCWE 002 C) NM 400 D) NRCWE 004 E) NM 402 F) NM 101 G) NM 110 H) NRCWE 003 I) NM 111 J) NRCWE 001. The LC20 ± one serial dilution has been used for the majority of NMs (NM 110, NM 111, NM 300, NM 400, NM 402, NRCWE 003 and NRCWE 004). For NMs in which an LC20 was not reached the three highest concentrations were utilised.